Telephone system



Nov. 9, 192a. 1,06,019

' H. D. CURMER ET'AL TELEPHONE SYSTEM Nov. 9, 1926. --l,60"6,0l9

H. D. CURRIER ET AL TELEPHONE SYSTEM EramZZZzzrrzler 55017952755757?Nov. 9, 1926. 1,606,019

H. D. CURRIER ET AL TELEPHONE SYSTEM Filed March 23. 1921 4 Sheets-$heet4 Patented Nov. 9, 15926.

nears stars were PATENT HIRAM D. CURRIER, OF CHICAGO, AND GEORGE E.EATON, OF OAK PARK, ILLINOIS, ASSIGNORS TO KELLOGG S'WITCHBOARD ANDSUPPLY COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE SYSTEM.

Application filed March 23, 1921.

Our invention relates to multi-oiiice systems, that is, systems in whichtwo or more exchanges are interconnected by means of trunk lines andtrunking calls between exchanges are handled over these wires byoperators in the originating exchange who pass the calls to operators inthe distant exchanges, which latter complete the connections to thecalled subscribers lines.

In the system of our invention we have abandoned the former practicewhich involved A operators cutting in on the B operators head telephoneover an order wire, passing the wanted number, the A operator thenreceiving the designation of the trunk to be used, and plugging intothat trunk with her calling cord, while the B operator plugged into thecalled line. In the system embodying our invention, the A operatorreaches the B operator by plugging in with the calling cord into a trunkjacket, and automatic selectingswitch mechanism then extends the call toan operator in the distant exchange, and namely to an idle operatorthere, and connects directly into her head telephone. This permits us todo away with B operators in the sense of operators who handle trunkcalls only and all operators in the system put up local calls which arecompleted in their own exchanges, and also serve as B operators in thesense that they receive calls transferred from distant exchanges andcomplete the connections required for such calls.

A particular feature of the present invention consists in this that whena trunking call has been completed from a calling subscriber in oneexchange to a line of a called subscriber'in a distant exchange, theinterofiice trunk is released and rendered available for further useinstantly upon the conclusion of conversation as a consequence of actsperformed at the connected substations. A considerably greater number oftrunking calls can thus be passed over each inter-office trunk than inthe previous systems in which the trunks are freed only by the operatorsthemselves, as it would frequently happen that an operator would be busywith other work and could not promptly take down a cord circuit whoseuse was finished.

Other features of the invention will be found in an improved system ofsignals for Serial No. 454,978.

the operators, and these and other particular items of novelty will beexplained in the description and pointed out in the claims.

e have illustrated our invention in a circuit diagram consisting ofFigure 1, which comprises parts 1, 2 and 8, while Figure 2 illustrates amodification of the invention.

Referring first to Figure 1, in part 1, We have illustrated asubscribers telephone line circuit and a cord circuit suitable forinterconnecting local subscribers lines within one exchange, which wehave designated B. The said cord circuit may also be used for trunkingcalls to distant exchanges, and when its calling plug CP is inserted ina trunk switch jack 67, (referring now to part 2) the automaticselecting switches C and D are set into operation to extend the callover the interoliice trunk wires :0 and 3 and land it at the distantexchange E (part 3) in the ear of some operator there who is not busy atthe time, that is, one who has not her head telephone cut in on someother local cord or trunk, for it will be understood that at exchange Ethe operator will be provided with local cord circuits identical incharacter with the one shown in Figure 1, part 1.

The system as a whole, therefore, may consist of two exchanges B and E,at which the operators will have identical equipment, that is, asuitable number of local cord circuits, such as shown in Figure 1, part1, and also a suitable number of trunking cord circuits, such as shownin Figure 1, part 3. Furthermore, before each operator will be suitabletrunk jackets 67 connected with switch pairs, such as O and D, so thatany operator at any exchange can in addition to establishing localconnections pass trunk calls to distant exchanges as well as receivetrunk calls from such distant exchanges.

To describe the various instrumentalities in a general way, at A we haveshown a common battery subscribers local substation connected atv theexchange with a usual form of line circuit comprising line relay LR andcut-off relay CO, together with multiple line lamps LL. The operatorscord circuit shown in Figure 1, part 1, comprises an an swering plug APand a calling plug GP, connected by talking wires which are indicated bythe heavily marked lines. It is provided with answering and callingsuper visorysignals and the necessary relays for controlling them andwith suitable relay apparatus for providing the various features nowconsidered necessary to a modern manually operated telephoneswitchboard, such as secret service, automatic ringing, instantaneousdisconnect, line lamp recall, etc.

The apparatus for transferring trunking calls from one exchange toanother includes a number of spring jacks 67 at each operators positionwhich terminate in multiple contacts located in a number of finderswitches as C, and one of these will automatically select a jack 67 inwhich an operator has inserted a plug, such insertion serving toinitiate the travel of an idle switch C. When the switch C has completedits operation, the switch 1) at the distant exchange will be set inmotion, and it comprises suitable magnets, relays and oftnormal springsto effect theautomatic selection of an idle trunk cord of the kind shownat E in part 3. y y

he latter has but a single plug 167 to which extend the talkingconductors indicated by the heavily marked line and suitablerelayinstrumentalities and circuits for testingg ringin and supervisingat the exchange E, an also for extending the required signals back overthe trunk line to the originating exchange B.

A more complete understanding of the -precise arrangement of the partsand their operation, one with the other, will be ob tained from thefollowing description of operation. i

\Ve will first assume that a subscriber at A desires to converse with acalled subscriber at F, the latters line ter'1ninating in an exchangedistant from exchange B to which the calling subscriber belongs. Theremoval of the receiver at A energizes relay LR lighting lamps LL, whichlamps are distributed at various positions in the switchboard. Anoperator seeing the lamp at her position displayed, will insert theanswering plug AP in a. jack of the calling line and re1ay16 instantlyenergizes by current through its two windings, normal contact 4,thesleeve plug and jack contact and through cutoil relay CO, the latteralso energizing and clearing the line for talking, as well as puttingout the lamps LL by tie-energizing the linerelay. The energizing relay16 by its contact 18 shunts out its high resistance upper winding sothat if another operator has plugged into another jack of the line of A,such other operators relay 16 will fail to energize because of the shuntestablished by the low resistance winding at the first operators relay16, and the second operatorgwill get no response when she asks for thenumber and will withdraw her plug. The operating relay 16 of the firstcord by its contact 19 energizes listening relay 7 b current flowing toground at 35, with the result that contacts 9 and 10 connect theoperators telephone set to the calling line and she inquires and learnsthe. number of the wanted subscriber. Furthermore, by the operation ofrelay 16, the supervisory relay 12 has been cut across the calling line,supplying talking current thereto, and by its armature 14 preventing thepremature display of supervisory signal 15, while its contact 13actuates counter relay 53, resulting in the actuation of magnet 54 tocount a call as answered by the o erator. The operator at B learningthat t e line of the wanted subscriber terminates at the exchange IE,will now insert calling plug GP into spring jack 67, such spring ackbeing assigned for calls to be extended to E, and she will first haveactuated her cutout key OK to close itscontacts 46 and 47. The insertingot plug OP has established an energizing circuit for the relay. 36extending through contact 5 of relay 1, the sleeve plu and jack contact,and to battery throng relay 68 at C, as well as an energizing circuitfor relay 34 in parallel with the one just described. As a result therelay 68 energizes and sets in travel the switch at C by closing itscontact 69 which grounds. starting wire SlV (which extends from switch Cas a common wire to all relays 68 connected with spring 'acks 67 adaptedto be selected by the switch C). Current will now flow from batterythrough the resistance r, motor magnet MM, normal contact 83 and theground through contact 69, and. magnet MM will energize and(ole-energize, stepping the switch wipers 75, 76, 77, and 78 a firststep from normal in search of terminals of the spring jack in which theplug has been inserted. On the first step the springs ON are shifted totheir alternate positions and successive actuations of magnet MM areproduced by its armature over a circuit through alternate contact ON, toground throu i contact 82 and 87. Such actuations will continue, eachcausing astep of the. wipers 75, 76, etc., until they engagemultiplejacks in their banks connected to a jack 67 in which a plug hasbeen placed, and which has not been already selected. As soon as thisoccurs the motor magnet MM will be shunted preventing its furtheractuation, and this shunt may be traced from battery through theresistance *1", the low resistance upper winding of relay 84, throughwiper contact 75, its engaged bank contact and through normal contact 74and alternate contact of relay 68 associated with the spring jack 67.The relay 84 attracts its armature contact 87 opening the circuit formagnet: MM, and energizing relay 79, while contact 86 connects therelays high resist ance lower winding in series with its upper windingand the relay locks to ground at 71, the circuit being traced throughwiper 76. The relay 72 energizes and opens its contact 74 so that noother switch whose wiper 75 engages a multiple of the seized contactwill stop, while the opening of contact 73 keeps ground ofi' thestarting wire SW, so that when relay 79, which is now energized, closedalternate contact 83 and thus extends starting wire SW to starting wireSLV which extends to another finder switch in the usual manner, thelatter will not be started. The relay 79 having energized as abovedescribed, locks itself to an off-normal ground by its contact 81 and by82 opens another contact in the circuit of magnet MM.

By the closure of contacts 85 and 88 of relay 84, the relay 9% in thedistant exchange has had its windings connected across the trunk wires00 and y, and current flows from battery through the upper winding of94, normal contact 90, over the heavily marked talking conductor via thetip contact of 67, UP, the alternate contact at 16, over the common wireto ground through the winding of the relay 55, while another circuit isestablished from battery through the other winding of relay 55, thealternate contact 17, to the right through the ring contacts GP, 67,over the talking conductor, and through normal contact 93 and the lowerwinding of relay 9% to ground, it being remembered that at the time theoperator at B inserted the calling plug she threw over the levers 46 and47 of her cut-out key. As a result, the relays 95 and both energized,and it is to be understood that the relay 55 is common to all cords of aposition. When the operator first threw over the levers of her cut-outkey, the closure of contact at 18 energized the relay 57, with theresult that a tone from the constantly operating interrupter mechanism61 was transmitted via contact 56 into the operators head telephonethrough the winding of her induc tion coil, and she thus had an audibleindication which was terminated when the relay 55 was energized as justdescribed, because the opening of contact 56 interrupted the tonecircuit. By the cutting ofi of this signal she knows that the switch Chas properly performed its function and has extended the call over thewires 50 and g to the distant exchange and that the switch D is startingits travel.

The starting of D is effected by the energization of relay 94: which byclosing contact 95 energizes motor magnet Mlil by current via normalcontact ON, and said magnet by a suitable pawl and ratchet mechanismsteps the wipers 10 1, 105 and 106 one step from normal to engage thefirst set of contacts leading to a trunk circuit, such as that shown atE. Upon this first step, the contacts ON are shifted and if the firstcontact engaged by wiper 104 is a busy contact, it will be grounded, theman ner of such grounding to be later explained. The result is that incase of such grounded contact a circuit will be established from batterythrough relay 102, the armature contact of magnet MM, contact 97,contact 91, the relay 101, and over wiper 104 to the engaged busycontact and to ground. Consequently, relays 102 and 101 energize and thelatter is of slow release construction so that rapid interruptions ofits circuit as the switch travels are not effective to cause itsarmature contact to restore. The opening of contact 103 tie-energizesmagnet MM whose retracted armature in turn de-energizes relay 102,whereupon magnet MM instantly is again energized by current through thenow closed contact 103, the alternate contact at ON, the contact 97 and91, the relay 101 and to ground, through the wiper 10 i and the engagedgrounded contact, whereupon magnet MM steps the wipers another step, andby the closure of its armature contact will again energize the relay 102over the previously described circuit to wiper 104: and now to ground tothe next engaged contact if it is busy. Thus a see-saw action betweenrelay 102 and magnet MM is produced, the slow relay 101 being in thecircuit of which ever one of the other two is energized, and thissee-saw action will continue until the wiper 104 engages a contact inits bank which leads to a trunk line in the exchange E which terminatesbefore an operator who is not busy, that is, who has not her headtelephone in use, then the see-saw action terminates because the engagedcontact of such a trunk line will be characterized by a freedom fromground. When this occurs the circuit will remain open through the slowrelay 101 whose armature will retract and energize the slow releaserelay 89 by current through contact 98 and to ground through the shiftedoffnormal contact. By the shifting of contacts 90 and 93 to engage theiralternate contacts a circuit is closed from battery through relay 55 atB over the lower heavily marked talking conductor to the right throughwiper 106 and its engaged idle contact, through winding 0 of theinduction coil at E in series through the two windings of relay 107,through winding a of the induc tion coil, to the left over the heavilymarked talking conductor, and through the lefthand winding of relay 55to ground. This energizes relay 107 and its armature 108 operates relay110 which closes contact 114 and grounds the contact engaged by thewiper 104: of the switch B, the result being that relay 89 at D by itsarmature Contact 91 locks to ground via relay 101 at contact 11 1. lVhenrelay 89 first operated the shifting of its contact 92 energized therelay 96 which was immediately locked to ground to the off-normalcontact via its armature Switch 99, and said relay 96 by opening contact98 opens the initial energizing circuit of relay 89, but the lattersslow release construction causes it to hold its armature in operatedposition until the substitute circuit oye'r wiper 104 was established,as just described. The relay 96 by means of switch contact 97 which hasnow opened, has effectively prevented any reoperation of motor magnet MMuntil the relay 96 is de-energized, which can only happen after theswitch D is restored to normal, and the con- I tacts ON are consequentlyshifted to their original position.

Referring now to the apparatus at E, the relay 110 (which energized asthe result of the closure of contact 108) energized relay 1'09 and alsorelay 116, which latter, by its contacts 117 and 121, connects theoperators relay 158 across the talking conductors, and said relay 158energized by current through the windings of relay at B over a pathwhich is obvious from the preceding description. As a consequence, theoperators talking set at 168 is connected into circuit with that of theoperator at B through the contacts 59 and at B. he operator at B nowtells the operator atE the number of the subscriber wanted, and thelatter plugs into a spring jack of the line, having first tested it inthe usual way and found it idle.

It will be observed that upon the energization of relay 110, the signallamp 152 was lighted by current flowing through alternate contact 112 sothat the operator at E knew which of her trunk circuits was to be usedin establishing the connection. The relay 116 (there being a relay 116for each cord circuit at the operators position) in addition to cuttingthe operators telephone relay 158 into circuit closed its armaturecontacts 118, 119, 120 to ground, and it is to be understood that theshort wires indicated at its armature contacts are connected to theprivate terminals of all trunks belonging to the operators positionwhose nead telephone is now out into use, so that as long as the relay116 remains energized no other switch D can connect effectively with anytrunk assigned to the said operator.

Furthermore, we have illustrated at H a relay 116 which is common to agroup of trunk circuits E and the relay 116 in con- 'unctio'n withrelays 116 of the trunk circuits l5 and the operators listening relays 7of the local cords shows clearly the exact wiring of this part of thesystem. It has al ready been stated that the operator at B is providedwith incoming trunks like that illustrated at E and the operator at Ehas not only incoming trunks E but is also provided with local cordcircuits B and it is to be understood that the wiring and interrelationof the local cord circuits and the trunk circuits at the variousoperators positions in both exchanges are alike. The relay 7 shown at His the listening relay 7 of a local cord circuit B located at E and theconnections from the armature contacts 8, 9, 10 and 11 are omitted forconvenience but it is to be understood from this diagram at H thatwhenever the listening relay 7 of any local cord circuit B is energizedthe operators head set is cut in and its alternate contact 166 is closedto connect ground thereto.

The alternate contacts 166 of the operators listening relays 7 of cordcircuits B of each operators position are multipled to a commonconductor CW which conductor CW extends to the winding of the relay 116which is common to a group of trunk circuits at E at this particularoperators position, it being understood that there is a relay 116 commonto each operators position and its group of trunk circuits E. Now whenthe operators telephone set is cut in on a calling line by means of anyrelay 7 of any of her local co'r'ds the closure of its alternate contact166 will place ground on the common conductor ClV which leads to therelay 116, and this ground will close an energizing circuit for relay116 common to the trunk circuits E associated with this operatorsposition. The relay 116 upon energization will close its alternatecontacts 161, 162, 163 and 164 and assuming that each operat'oi"sposition isequipped with four trunk circuits such as E the closure ofthese four alternate contacts will ground the private contacts of thefour trunks at the switches D and prevent any of the trunks from beingselected so that it is impossible for the operators telephone set to becon nected in on two different calls at the same time and from the abovedescription it is also seen that a trunk call will only land at anoperators position whose telephone set is idle at the time the switchengages the trunk.

\Ve left the operator. at E just having received the number of thecalled subscriber I from the operator at B. The latter now restores herout out key with the result that the windings of the calling supervisoryrelay CSR are substituted in the circuit of the windings ot' the relay55. and the relay 57 7 her out out key CK, closes its contacts 46 and47, and a circuit is closed for relay CSR which may be traced frombattery, through its lower winding and over the heavily marked talkingconductor to E, through winding 0 of the repeating coil to the right, toconnect to the armature 129 of relay 127, through normal contact 180,thence through the lower winding of relay 107 through winding a of theinduction coil to the left, over the talking wire and through the upperwinding of the relay CSR to ground at 38. Thus it will be seen that theupper or high resistance winding of the relay 107 is short-circuited,and consequently, relay CSR at B receives enough current to energize itto actuate its armature, and contact 32 is opened, thereby preventingthe display of signal 28 so that we have the dark key shelf feature.

The operator then having found the called line idle inserts her plug 167in a multiple jack of that line, the immediate result being theenergization of relay 122 in. the trunk circuit and of cutoff relay COof the called line circuit, which latter relay clears the line. Relay122 by contact 126 de-energizes relay 116, whose retracted armaturecontacts 117 and 121 disconnect the operators head telephone, while itsother armatures unground the terminals of the other idle trunks at theposition rendering them selectable by switches D. The master groundcontact MG at 122 is now closed operating the relay 133 by currenttraversing the. contact 113 at relay 110, and the armature 136 puts outthe signal at 152 and locks the relay 133 to ground at contact 112 ofrelay 110, while contact 135 establishes another locking circuit for therelay 133 extending to the master ground MG. The contact 137 operatesthe counter magnet 157 to count a completed trunk call for the operatorat E and relay 138 immediately thereafter opens contact 139 to preventany possible reoperation of the counter magnet.

Assuming that the substation F has a harmonic bell, the operator willnow actuate her ringing key button to close one of the contacts 155 ofher ringing key, and will select the one connected to the generator ofproper frequency, and in so doing will momentarily close the end spring154, which latter spring will close a circuit to energize relay 140 bycurrent through said relay and said spring, and contact 132 over groundwire GW to ground at MG, said relay 140 by its contact 142 lockingitself to ground at MG via the normal contact at 150. The result of theclosing of contact 141 of relay 140 is that the relay 144 is connectedin circuit with the constantly rotating interrupter 159, and said relay144 will alternately energize and deenergize, attracting and releasingits contacts 146 and 147 to connect and disconnect generator from thecalled line to periodically ring the bell at the substation, the path ofthe ringing current being traced through a contact 155 (the contactremaining closed after being once operated, although the end contact 154restores as soon as the operator removes her hand from the button), thewinding of the relay 149, alternate contact 147, tip plug and jack at167, through condenser and call bell at the substation, back through thering contact at 167 and to battery at alternate contact 146. If during aringing interval, the called subscriber removes his receiver at thesubstation, the slow release relay 149 will receive enough current toactuate its armature to open contact at 150 and this will de-energizerelay 140 by opening its locking circuit and the relay 144 will have itsconnection with interrupter 159 opened at contact 141, and will remainde-energized so that no longer can ringing current be applied to thecalled line. As soon as contacts 146 and 147 are closed after thesubscriber removes his receiver, or if they are closed at the time hedoes so, the relay 127 is energized by current from battery through itslower winding, through winding (Z of the induction coil, over the ringplug and jack contact at 167, the switch hook contact at F, back throughthe tip plug and jack contact at 167, normal contact 147, alternatecontact 123, winding 6, the upper winding of said relay 127- to ground.Contact 128 of relay 127 now closes a circuit which energizes relay 130by current over the ground wire GVV, and said relay 130 by its contact131 locks itself to said ground, and by opening contact 132 cuts off allthe ringing key apparatus and relays definitely from the ground wire.lVhen on the response of the called subscriber the relays 127 and 130operate as just described, the relay 130 opens the short circuit aboutthe upper winding of the relay 107, but before it does so, the relay 127by its contact 129 has provided another shunt about the upper winding sothat the lamp 28 remains dark while the subscribers are talking.

The subscribers at A and F are now in conversation, the talking circuitbeing traced from A to F over the heavily marked conductors, thetransmitter of the substation at A receiving its current through thewind ings of relay 12, while the transmitter at F receives its currentthrough the windings of relay 127.

hen the subscribers have finished conversation they replace theirreceivers, and we will assume that the subscriber at A does so first. Heconsequently opens the circuit of his answering supervisory relay 12 andthe lamp 15 is displayed by current through normal contact 14, alternatecontact 20, to ground through alternate contact 35. Furthermore, thebust relay 1 is, operated by [ill cuia ent through it and traced toground through the same contacts 20 and 35, and said relay 1 by itsarmatures 2 and 6 opens up the talking conductors of the cord strands;by its contact 4, it places the sleeve contact of the plug on opencircuit, thus removing the busy test from the multiple jacksof the lineof A, and in so doing deenergizes cut-ofi' relay G which now places theline relay LR under substation control. The closure of alternate contactat 4. maintains the relay 16 operated, however, a substitute lockingcircuit for said relay being traced through contacts 20 and 35 toground. The opening of contact of relay 1 would deenergize the sleeverelay 36 at the calling end of the cord were it not for the fact thatrelay CSR is still energized, because the called subscriber is assumednot to have replaced his receiver as yet, and the closed contact 33keeps the winding of relay 36 operatively connected to the sleeve strandof the cord extending to plug Cl Now when the called subscriber at F atthe end, of conversation replaces his receiver before the subscriber atA, the resulting de-energization of relay 127 by the opening of itscircuit at the substation switch hook, will serve to open the contact129, and since the relay 130 will remain energized by current throughits locking armature 131, the only path for current through the windingof relay CSR at B will be through the two windings of the relay 107 atE, and this current will be so slight that relay ,CSR will retract itsarmature to light the lamp 28. The relay 36 is thus wholly disconnectedfrom the Sleeve strand of the cord, and consequently de-energizedopening the talking conductor of the cord circuit at contacts 37 and 40.

It will be. seen that as soon as the relay 36 is cut oil from the sleevestrand of the cord, the only battery connection to said cord strand isthrough the winding oi rc lay 34, which relay is of very substantialresistance, for instance, 7000 to 7500 oluus. Current continues flowingthrough said lay and through, the sleeve contact at C1 67, to ground,through relay 68 at C, and this current is sullicient to maintain therelay 34 operated but the relay 68 owlng [0 its relatively ineliicientconstruction and the adjustment'of its armature, aliows its armaturecontacts ,to be opened, and this results in the restoration of theswitches C and D as follows: The opening of contact 71 opens the lockingcircuit of relay 84, which (le -energizes and in so doing opens thetalking .i'vires extending to wipers 77 and 78 at contact 85 and 88, andby closing normal. contact 87 energizes release magnet RM by currentthrough alternate contact 82 of relay .79, and said release magnet RMwithdraws the retaining pawl of the switch and the wipers areSpring-restored to normal. The

opening of contact 71, of course, has deen ergized relay 72, while therestoration to zero of the switch has placed contacts ON in their normalposition, and all the mechanism at C is now at normal.

On the opening of contacts 85 and 88, the. relay 107 at i") has itscircuit opened, and consequently is (lo-energized. The rctrao tion ofits armature de-energizes relay 110. the latter by restoring armature115 de-cn ergizing the relay 109. The opening of contact 114 removesground from wiper at E, and as the relay 109 is relatively sluggish torestore, it will keep its armature attracted long enough to insure thatthe relay St) at D will allow its armature to tall back, wherebycontacts 90 and 93 place the tall:- iug wipers 105 and 106 on opencircuit, while- 92 falling back energizes release magnet RM by currentfrom battery through said magnet, cont-act 100, normal contact 92, toground through the shifted contact ON, and said magnet Rivl withdrawsthe retaining pawl of the switch 1) which r'springrestored to its zeropoint, at which time the contacts ON open tie-energizing relays 96 andmagnet RM, and the apparatus oi the switch is at normal.

It is thus seen that when the two subscribers have replaced theirreceivers, the 95 two switches C and D are released and fully restored,and this is very important inasmuch as it trees the trunk wires m, 3which extend from one exchange to another, (usually involving a verysubstantial investment in capital) so that the freeing of them and therendering of them promptly available for another connection is an itemof the greatest importance in the economical operation of a telephonesystem.

The operator at B seeing the signal lamps and 28 displayed, withdrawsthe plugs AP and GP which (lo-energizes the relay 3-4;, which in turntie-energizes relay 1, and the apparatus and cord circuit are at normal.

It is (it course obvious that the relay 1 when it first energizer gavethe calling subscriber the advantages of instantaneous d3" connect andline lamp recall, irrespective of the Withdrawal of the plug AP.

The dc-encrgization, of relay 110 at E as above described results in thel ghting of the SllpGlVlSOl'y lamp S, and theoperatcr at E observing thes gnal withdraws the plug 167 to dc-energize relay 1.222 of the cord,and by the shifting of its contacts including that of master ground MG,the up paratus oi. the trunk cord is placed at nor-- .mal, while thewithdrawal of the plug 167 has restored the line circuit at F byde-energizing line relay CO.

Lamp 1.53 in the trim}: circuit E increly a guard lamp which is lightedas soon as master ground MG is connected up, the said lamp being lightedindicating to the oper" ator that she has not actuated her ringing keylever to ring the called subscriber. As soon as she does so closingcontact 154, the relay 140 energizes and locks puts out the lamp 153.

Let it be asunned that although the called substation bell was rung, thecalled subscriber did not answer the call. In such case the callingsubscriber will replace his receiver and de-euergize relay 12 toenergize relay 1. Relay 36 is then cut oil from the cord strand and itis plain from the preceding that switch G will restore.

Circuit being opened thereby at wipers 7'l78, relay 107 at Edeenergizes, and as a consequence relay 110. The supervisory lamp S at Ewill now be lighted and the operator will pull out plug 167.

Let it be assumed now that a calling subscriber at A removes hisreceiver to initiate a call for a subscriber in his own exchange. Theoperation of the line circuit and cord circuit of Figure 1, part 1,would be the same as that already described until after the operator hasreceived the number 01" the called subscriber. In this case, she wouldtest a multiple spring jack of the called subscribers line whose linecircuit and substation would have exactly the same arrangement as thatof the subscriber A. To make the test the operator touches the tip or"the plug GP to the sleeve of a jack of the called line, and if thisspring jack is busy because a plug of another cord circuit has alreadybeen 3 placed in a multiple of the jack tested (pro vided always thatthe subscribers have not effected the automatic disconnect), there willbe apotential above ground at the tested sleeve contact and an impulseof current will flow through the tip of plug GP, normal contacts 46-42the closed contact 8 of relay 7, and to ground through the test relay 62which is common to an operators position, and said relay will actuateits armature 63 to close battery through the tertiary winding of theoperators induction coil, giving her the customary busy click.

Moreover, the test arrangement provides means for giving the operator arevertive tone test, it she tests a spring jack of the line in which shehas already inserted the answering plug of the cord, that is, if thecalling subscriber want-s another subscriber on his own line, the systemthus providing for the case in which there are a number of substationsconnected to a single line. In making such a revertive test the operatorwill receive the click as usual, but in addition the closure or" contact64 will connect the revertive tone test apparatus to the operators headtelephone, the circuit being traced through contact 64, contact 11,normal contact 4, through the sleeve contact or plug AP to the sleeve ofthe jack in which that plug is inserted, thence to the sleeve of callingplug GP and ring in the usual man-,

ner.

But assuming now that the substation called for is on an idle lineentirely independent of that of the subscriber at A, the operatorreceiving no click upon her test, inserts the calling plug GP in thetested jack, thus placing the relays 36 and 34 oi her cord circuit inconnection with ground through the winding of cut-oft relay GO of thecalled line, and said relays 36 and 34 are both operated with results tothe switching instrumentalities of the calling end of the cord circuitas previously described herein, and the cut-oil relay GO of the calledline will o1 course energize to clear the line circuit for talking andringing, the line relay LR being disconnected. The operator at B nowactuates whichever ringing key lever 49 will impress current to theproper frequencyto ring the bell of the called substation, the leverstaying in its shifted position, while the end springs 51 and 52 of theringing key are shifted to close their contacts but only as long as theoperator holds the ringing button down. By the closing of contact 52,the relay 22 energizes over a circuit which may be traced through saidcontact, through contacts 3, 30, 82, and alternate contact 35 to groundand said relay 22 by its contact 26 locks itself to ground at By theclosure of contact 51 the upper winding of the ringing relay 41 receivescurrent which goes to ground of contact 25 of relay 22 so that thecalled substation is instantly rung and will continue to be rung as longas the operator keeps the levers 51 and 52 shifted. When she releasesthe button said levers restore to normal, and the upper winding of relay41 is disconnected, but the lower winding of said relay by the closingof contact 24 of relay has been connected with the constantly operatinginterrupter I and will alternately be energized and de-energized,cutting in and out the selected ringing generator. The flow of ringingcurrent is to be traced from ground through the generator sel cted, theshifted lever 49, lower winding of relay 29, alternate contact 42, whenrelay 41 is energized, contact 46, the tip plug and jack contact,through the called subscriber and its bell, back to the ring plug andjack contacts and to battery at alternate contact 45. If the subscriberanswers in a ringing interval the reduced resistance at his substationcaused by the removal of his receiver will now open.

allow sufficient current to flow through the lower windin of relav 29 toener ize it it D u b having previously remained inert because of thehigh resistance call bell circuit at the substation), and the said relay29 by opening its contact at 30, tie-energizes the relay 22 by openingits locking circuit extending to ground at 85 and the said relay 22restores not to reoperate because the contact 52 is Its retractedarmature contacts 23 and 27 reestablish the talking circuit at thesepoints and the opening of contact 24: prevents any further operation ofringing relay 41, which relay deenergizes, and the contacts 42 and 45complete the talking circuit between the subscribers. The closing ofcontacts 42 and also connects the two windings of calling supervisoryrelay CSR to the called for line and it energizes, since the substationreceiver has been removed.

If the called subscriber had removed his receiver during a silentinterval, the contacts 42 and would then have been closed and relay CSRwould instantly have energized over called for line, and by opening itscontact 32, would have tie-energized the relay 22 with results asbefore.

The calling and called subscribers are now in conversation, and, whenthey have finished they replace their receivers. It will. be assumedthat the called for subscriber does so first. The opening of thetransmitter circuit through the substation tie-energizes relay CSR andits retracted armature, contact 32 will cause the lamp 28 to be lightedby closing the circuit of said lamp to ground at alternate contactNothing further results at this time, but when the calling subscriber Areplaces his receiver, the resulting de-energization of relay 12 by therestoring of contact 14 energizes the relay 1 by current flowing toground at alternate contact 35, and by its armatures 2, 4, and 6 allthree contacts of plug AP are placed on open circuit so that the line ofthe calling subscriber is restored to its normal condition as far assignaling and testing purposes go. It will be observed that the closingof alternate contact 4 of relay 1 establishes a substitute lockingcircuit for the relay 16 before said relays arinatures have time toretract, said substitute circuit being traceable through alternatecontact 20 and to ground at alternate contact One circuit through thesleeve relay 36 has already been opened at contact 33 of relay CSR, andthe opening of contact 5 at relay 1 opens the other circuit through saidrelay 36 so that the said relay now deenergizes. The onlyinstrumentality now in circuit with the cut-off relay of the called forline is the relay 34 which is of so high resistance, say between 7000and 7500 ohms, that'sufficient current does not flow therethrough andthrough the called cut-off relay CO to enable the latter to retain itsarmature attracted, although due to its greater efiiciency, the relay 34continues to hold alternate contact closed. The result is that therestoration of the contacts of relay ()0 of the called for line placesthe line circuit of the said line under control of the substation switchhook so that the substation is provided with line lamp recall service atthis time, and the said line will furthermore test idle at this timebecause of the high resistance of the relay 34 which results in apotent-ial so slight upon the multiple jacks of the called line as tomake the operators test ineffective if some operator tests that line.

Both lines are now free and the lamps 28 and 15 are both displayed andthe operator withdraws the two plugs, and restores all apparatus of thecord circuit to its normal condition.

if the calling subscriber had replaced his receiver before the calledfor subscriber did so, relay 12 would be tie-energized and the callingline would, by the resulting operation of relay 1, instantly have beengiven disconnection and recall as before. The called for line, however,would not be free until the called for subscriber replaced his receiverfor the reason that the relay CSR would remain operated until that time,and by its contact 33 would hold the relay 36 in circuit with thecut-off relay C0 of the called for line. hen, however, the called forsubscriber did replace his receiver, his line would be freed in thedescribed obvious way.

It will be noted that the circuit of the calling supervisory lamp 28 isled through the back contact 26 of relay 22, and as the said relay isenergized when the operator depresses her ringing button, the lamp is atthat time put out and remains out until the called for subscriberreplaces his receiver when the lamp is lighted, either through itsoriginal energizing circuit, namely, via the back contact at 26, or ifthe calling subscriber has already replaeed his receiver, the said lamp28 will be energized by current through alternate contact 3 of relay 1.We thus have what is known as the dark key shelf method of operation.

Referring now to Figure 2, we have illustrated a cord circuit which maybe substituted throughout the operation of the system as hereinbeforedescribed, for that shown in Figure 1, part 1. Corresponding relays havebeen given corresponding reference characters, and it is not consideredthat a detailed description of this circuit is at all required in viewof what has already been said in connection with the cord circuitsillustrated in Figure 1, part 1.

Particular attention is however called to the relation in Figure 2established between the relays 36 and 3-1. It will be noted that relay36 is here connected permanently in series between the winding of therelay 34 and the live side of the central source of current. In additionto this connection which results in the relay 36 being permanentlyconnected to the sleeve strand of the cord circuit, the winding of saidrelay is connected to two branch Wires, one controlled by the lowercontact of the calling supervisoryrelay CSR, while the other iscontrolled by the lower contact of the relay 1. In accordance with thisarrangement, when the relay CSR de-energizes at the end of conversation,it will open one circuit through the relay 36, and when the relay 1 isenergized it will open another circuit through the relay 36, the pointscontrolled by these two relays CSR and 1 being intermediate between thewinding of the said relay and the sleeve strand of the cord circuit. Inaccordance with the arrangement of Figure 2, however, this will notresult in depriving the relay 36 fully of current because it ispermanently connected to the sleeve strand of the cord circuit throughthe winding of the relay 84. Owing, however, to the very high resistanceof the latter relay, which we have already mentioned as being desirablybetween 7000 and 7500 ohms resistance,-

the flow of current through the relay 36 at this time will be so veryslight that the said relay will not maintain its armature in itsattracted position, but on the contrary will allow it to restore. Therelay 34 will remain energized with the same result as heretoforeexplained, and the cut-oil relay of the line will also de-energize asbefore.

lVhile we have illustrated and described aparticular embodiment of ourinvention, it is to be understood that it is of considerable scope, andwe do not intend to be limited to the particular devices and connectionsherein shown and described, but intend to include all such modificationsas will suggest themselves to those skilled in the art, and to claim theinvention in its general aspects.

Having described our invention what we claim as new and desire to secureby United States Letters Patent is:

1. In a telephone system a pair of connected telephone lines, link andtrunk, circuits having terminals applied to the calling and called linesrespectively and rendering them busy, an automatic n-on-preselectingswitch interconnecting said first circuits by means 01. a third linkcircuit, means controlled by the subscribers to restore said switchwhile said link and trunk circuits remain connected to said lines and asignal for said link circuit inert during the extension of a connectionto a called line and controllable by said called line only upontermination of conversation.

2. In a telephone system a pair or" connected telephone lines, linkcircuits having terminals applied to the calling and called linesrespectively and rendering them busy, disconnect means associated withthe terminal applied to the calling line, an automatic selecting switchinterconnecting said first circuits by means of a third link circuit,means controlled by the subscribers to restore said switch withoutrestoring said terminals, said disconnect means operated by said callingsubscriber to free his line from said terminal applied thereto prior todisconnection of said terminal.

3. A telephone system comprising a calling line, a link circuit havingan automatic selecting switch provided with bank contacts and wipers,said switch operable to cause its wipers to engage certain contacts insaid bank contacts to extend the circuit of the calling line, meansincluding a manually operated terminal to extend said line to saidcircuit, a called line and switching contacts at the substations of saidlines effective to restore said selecting switch while said manuallyoperated terminal is connected with said line and a signal for saidmeans inert during the extension of a connection to said called line andcontrollable by said called line only upon the termination ofconversation.

i. A telephone system including a pair of connected telephone lines anda link circuit having an automatic traveling switch provided with bankcontacts and spring restored wipers for engaging said bank contactsthrough which bank contacts and wipers the connection extends, plug andjack connections one for each line and connecting its respective line tosaid circuit switching means operated from the substations and includingcircuits through said plug and jack connections for restoring saidcircuit switch and a signal associated with the plug and jack connectionof the calling line controlled by said called line to indicate thecondition of said called line.

5. A telephone system including a pair of connected lines, theconnection including non-preselecting traveling switch mechanism andplug connections one on each side of such mechanism, means controlledfrom the calling station to automatically restore said mechanism and asignal associated with one of said plug connections inert during theextension of a connection to said called line and controllable by saidcalled line only upon the termination of conversation.

6. A telephone system including a pair of connected lines, theconnection including non-preselecting traveling switch mechanism andplug connections one on-each side of such mechanism, means cooperativelycontrolled from the calling and called stations to automaticallyrest-ore said mechanism and a signal associated with the plug and jackconnection of the callingstation inert during the extension of aconnection to said called line and controllable by said called line onlyupon the termination of conversation.

7. A telephone system including a pair of connected lines, theconnection including rotary traveling switch mechanism having individualdriving means and plug connections one on each side of such mechanism,and means controlled from the calling station to automatically restoresaid mechanism, said means including a device for changing the testcondition of the calling line while the associated plug connectionremains.

8. A telephone system including a pair of connected lines, theconnection including non-numerical switch mechanism having individualdriving-means and plug connections one on each side of such mechanism,and

means cooperatively controlled from the calling and called stations toauton'iatically restore said mechanism, said means including a devicefor changing the test condition of the calling line while the associatedplug connection remains.

9. A telephone system including a pair of connected lines, theconnection including a link circuit having an automatically selectingswitch at each end, said switches having stationary bank contacts andtraveling contact mechanism adapted to engage said stationary contactsand said switches operative to establish the connection through theirrespective bank contacts and contact mechanism, plug connections onebetween each switch and the associated line, means controlled from acalling or called station over a plug connection for restoring saidswitches to their respective zero points and a signal associated withthe plug connection of the calling line inert during the extension of aconnection to said called line and controllable by said called line onlyupon the termination of conversation.

1 0. A telephone system including a pair of connected lines, theconnection including a link circuit having an automatically selectingswitch at each end, said switches having traveling contact mechanismoperative in establishing the connection, plug connections one betweeneach switch and the associated line, a signal associated with the plugconnect-ion of'the calling line controlled by said called line forindicating the condition of saidcalled line, and means controlled overthe calling line only for restoring said switches to their respectivezero points prior to the response of the called nection, plugconnections one between each switch and the associated line, and asignal associated with the plug connection of the calling linecontrolled by said called line for indicating the condition of saidcalled line, and means controlled over a plug con nection for restoringsaid switches to their respective zero points, said telephonesystemincluding also devices operative by the response of the called stationto change the control of said means.

12. A telephone system including a pair of connected lines, theconnection including a link circuit having an automatically selectingswitch at each end, said switches having traveling contact mechanismoperative in establishing the connection, plug connections one betweeneach switch and the associated line, and means controlled over thecalling line only for restoring said switches to their respective zeropoints prior to the response of the called for subscriber, saidtelephone system including also devices operative by the response of thecalled station to change the control of said means.

13. A telephone system including a pair of lines teri'ninating inmultiple line jacks and line signals before a number of operators andconnected by a link circuit having an automatic selecting switchat eachend, plug connections one between each switch and the associated line,one switch operated when connection is made by a plug connection "from acalling line to select said line said other switch operatingautomatically to select said other plug connection, a supervisory signalassociated with the lug connection of the calling line opera le from thecalled station when the receiver is replaced to change its indication,and connections preventing any changes in the indication of said signalwhen the subscriber answers the call.

14. A telephone system including a calling telephone line terminating inline jacks and line signals before a plurality of operators, a manuallink circuit connected therewith via one of said multiple line jacks andhaving a manually operated terminal, a calling and a called signal forsaid link circuit, means including automatic-selecting switch mechanismfor extending connection from saidcircuit to a called line, means forpreventing display of said called signal when connection is made to thecalled line and prior to response at the substation, and a switchhookeffective on replacement of the receiver to display said signal.

15. A telephone system including a-called line terminating in multipleline jacks and signals and a calling line terminating in multiple linejacks and signals, a manually operated link circuit for connectin saidline in circuit via one of said multip e line jacks, automatic selectingand connecting switch mechanism included in such connection, anoperators position on said connection having a calling and a calledsupervisory signal therefor, switching devices preventing a change inthe indication of said called signal when the called subscriber answers,and apparatus effective to change its indication when said subscriberreplaces his receiver.

16. A telephone system including a calling telephone line terminating inmultiple line jacks and line signals, an operators cord terminal inconnection with said line via one of said multiple line jacks, a distantoperators position and means including automatic selecting mechanism forconnecting from said cord terminal to an operator controlled switchatsaid position, a signal for said cordterminal, means for preventingitsdisplay when connection is extended to said distant position and aswitch controlled at a connected called station effective to displaysaid signal when the subscriber replaces his receiver.

17 In a telephone system a telephone line, a link circuit having aterminal in connection with said line, an automatic selecting switch forselecting said link circuit to extend the circuit of said terminal,means at the substation of said line to change resistance at saidterminal to restore said switch and a supervisory signal associated withsaid link circuit inert during the extension of a connection to a calledline and .line, said switch and its associated link circuit extendingthe circuit of said terminal, a predetermined flow of current through acontact of said terminal while connection exists, and relay meansoperable under substation control to create a lesser flow of currentthrough said contact to restore said switch.

19. In a telephone system a telephone line terminating in multiple linejacks and line signals, a link circuit temporarily applied with saidline Via one of said multiple line jacks, a second link circuitconnected to said first link circuit, and an automatic traveling switchoperable to select and to interconnect said circuits when said firstlink circuit is applied to said telephone line, and a signal for saidlink circuit inert during the extension of a connection to a called lineand controllable by said called line only upon termination ofconversation.

Signed by'us at Chicago, in the county of Cook and State of Illinois,this 18 day of March, 1921.

I-IIRAM D. CURRIER. GEORGE R. EATON.

